Phage therapy to reduce pre-proccessing Salmonella infections in market-weight swine

Authors: WALL, SAMANTHA - Purdue University; ZHANG, JIAYI - Purdue University; Rostagno, Marcos; EBNER, PAUL - Purdue University

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2009
Publication Date: 1/1/2010
Citation: Wall, S.K., Zhang, J., Rostagno, M.H., Ebner, P.D. 2010. Phage therapy to reduce pre-proccessing Salmonella infections in market-weight swine. Applied and Environmental Microbiology. 76(1):48-53.

Interpretive Summary: Contamination of meat and meat products with foodborne pathogens is usually the result of the carcass coming in contact with the feces of an infected animal during processing. In the case of Salmonella, several recent studies have reported that pigs become rapidly infected with the organism during pre-slaughter lairage due to contaminated holding pens. These infections serve to increase the likelihood of carcass contamination by amplifying the amount of bacteria that enters the processing facility. We conducted a series of experiments to test whether phage therapy could be used to counteract Salmonella infections at this crucial period. Fourteen anti-Salmonella phages were isolated from various wastewater treatment facilities. A preliminary experiment with young pigs (3-4 weeks) showed that administration of the anti-Salmonella phage cocktail at the time of inoculation with Salmonella Typhimurium reduced the infection in the tonsils, ileum, and cecum as compared to mock-treated pigs. To test the efficacy of phage therapy in a more realistic conditions, we inoculated four market weight pigs with Salmonella Typhimurium and allowed the infected pigs to contaminate a holding pen for 48 hours. At 48 hours post-inoculation, 16 market-weight pigs were randomly split into two groups that received either the anti-Salmonella phage cocktail (orally) or a mock-treatment. Both groups of pigs were then comingled with the infected seeder pigs in the contaminated pen. All pigs were euthanized for necropsy at six hours post-exposure. This experiment was repeated 3 times. Treatment with the anti-Salmonella phage cocktail significantly reduced cecal Salmonella counts, while also showing a strong tendency to reduce ileal Salmonella counts. Additional in vitro studies showed that the phage cocktail was also highly lytic against non-Typhimurium serovars such as Dublin and Enteriditis, and to a lesser extent, Lichfield and Schwartzengrand. The phage cocktail did not lyse serovars Indiana, Kentucky, Tennessee and Seftenberg. It is concluded that phage therapy can be used as an effective anti-Salmonella intervention strategy to prevent lairage-associated increases in Salmonella infections in pigs.

Technical Abstract: Contamination of meat and meat products with foodborne pathogens is usually the result of the carcass coming in contact with the feces of an infected animal during processing. In the case of Salmonella, several recent studies have reported that pigs become rapidly infected with the organism during pre-slaughter lairage due to contaminated holding pens. These infections serve to increase the likelihood of carcass contamination by amplifying the amount of bacteria that enters the processing facility. We conducted a series of experiments to test whether phage therapy could be used to counteract Salmonella infections at this crucial period. Fourteen anti-Salmonella phages were isolated from various wastewater treatment facilities and characterized by electron microscopy. Prior to administration to pigs, the phage were microencapsulated using a sodium alginate-lysine method. A preliminary experiment with young pigs (3-4 weeks) showed that administration of the anti-Salmonella phage cocktail at the time of inoculation with Salmonella Typhimurium reduced the infection by 99.0-99.9% (2-3 log) in the tonsils, ileum, and cecum as compared to mock-treated pigs. To test the efficacy of phage therapy in a more realistic conditions, we inoculated four market weight pigs (in three replicates) with Salmonella Typhimurium and allowed the infected pigs to contaminate a holding pen for 48 hours. At 48 hours post-inoculation, 16 market-weight pigs (in three replicates) were randomly split into two groups that received either the anti-Salmonella phage cocktail (orally) or a mock-treatment. Both groups of pigs were then comingled with the infected seeder pigs in the contaminated pen. All pigs were euthanized for necropsy at six hours post-exposure. Treatment with the anti-Salmonella phage cocktail significantly reduced cecal Salmonella counts (95%, P < .05) while also showing a strong tendency to reduce ileal Salmonella counts (90%, P = .06). Additional in vitro studies showed that the phage cocktail was also highly lytic against non-Typhimurium serovars such as Dublin and Enteriditis, and to a lesser extent, Lichfield and Schwartzengrand. The phage cocktail did not lyse serovars Indiana, Kentucky, Tennessee and Seftenberg. It is concluded that phage therapy can be used as an effective anti-Salmonella intervention strategy to prevent lairage-associated increases in Salmonella infections in pigs.